The present invention relates to a semiconductor device, and more particularly, to a method for correcting a layout with a pitch change section.
A nonvolatile memory device applies a line-and-space type layout frequently as compared with a Dynamic Random Access Memory device or a logic circuit. In order to perform a pattern transfer of such line-and-space type layout to a wafer more sophisticatedly, it is intended to implement a higher resolution using an asymmetrical illumination system such as a dipole illumination system. Though the line-and-space type layout can be designed to have an equal pitch, it can be designed by applying two different pitches for two different circuit areas. In such a case, the pitch of the line-and-space pattern can be changed in the boundary area of the different pitch areas.
In a section where the pattern pitch is changed in the layout, the line-and-space pattern is designed to be extended successively from an area at which relatively smaller pitch is applied to another area at which relatively bigger pitch is applied. For example, the flash element can be configured with a memory cell area and a page buffer area adjacent to it, and signal lines extended across these two areas, i.e., bit lines are formed with the line-and-space pattern. At this time, the pitch of the signal line in the memory cell area and the pitch of the signal line in the page buffer area are set different from each other. In the page buffer area, since the signal lines as well as high voltage NMOS contact must be disposed between the signal lines, the pitch of the signal lines in the page buffer area is disposed so that it will be changed to be larger. Consequently, the layout of signal line in the boundary area of the page buffer area and the cell area is designed to have a curvature or is connected to have different line width so that the layout is changed to have a step shape. Therefore, such boundary area can be set as a section at where the pitch of the signal line is changed, i.e., a pitch change section.
FIG. 1 and FIG. 2 are drawings showing a pitch change section of a pattern. FIG. 3a and FIG. 3b are drawings showing a layout and reticle which performs an optical proximity correction (OPC) on the pitch change section of FIG. 2.
Upon forming the pattern of the nonvolatile memory device, it is preferable to structure the layout in such a manner that a uniform pitch is successive without changing the pitch of the pattern. When applying the layout in which the pitch of the pattern does not change, it is possible to easily and correctly form a desired pattern on the wafer. However, when inserting a circuit such as a high voltage NMOS contact into a circuit necessary to operate the device, e.g., page buffer area, the layout is inevitably configured with the pitch change section at which different line widths are included. When processing the exposure operation by applying such layout and asymmetric illumination system, a contrast is reduced in the pitch change section 100, 105 and at the same time a defect such as a bridge or a pinching can be caused, as shown in FIG. 1 and FIG. 2. Such defect is considered to be caused due to the resolution reduction and an aerial image intensity discontinuity as different diffraction information is overlapped in the pitch change section.
Consequently, the optical proximity correct (OPC) is processed in order to overcome the patterning defect induced in the pitch change section. The OPC is the process of changing the layout of the problematic section considering the optical proximity effect. Referring to FIG. 2 and FIG. 3a, the OPC is processed in a manner that a shape of the layout is modified considering the optical proximity effect on the layout of the pitch change section 105 at which the defect is generated. However, the OPC has a problem in that the shape of the layout is complicated while reflecting the optical proximity effect on the layout. Referring to FIG. 3b showing the pattern on the reticle with the layout (FIG. 3a) on which the OPC is performed, it will be appreciated that the layout of the pitch change section 105 is complicatedly formed. Since the layout on which the OPC is performed is formed with a complicated profile, a mask writing equipment cannot assure a fidelity of the design layout. Further, it can be implemented differently from design intention in accordance with a state of the mask writing equipment or a fracturing state. As well, since an operation of modifying the layout of the pitch change section is dependent on manual operation by an operator, there is a disadvantage in that it takes much time and effort and it is difficult to ensure a stability on the process.